[Lalaith]

Lord Melkor, I'm extremly impressed by your grasp of Middle Earth geo-politics which far exceeds mine, but I feel you are starting from a premise that the various territories and kingdoms needed to be brought under Elessar's rule by force.
I think Tolkien's view was of a consenting federation. If you want an analogy, look at the European Union, after the fall of the Iron Curtain. No-one is forcing anyone to be part of it, but there's countries of the former Eastern Bloc, and now the near East: Turkey, Cyprus etc, clamouring to get in because the EU is prosperous and peaceful and by and large, it makes good economic sense to join.
Or, if you want to get more mediaeval, there was the Hanseatic League, which was a similar and most popular arrangement...